Field of the Invention
This invention relates to an electronic typewriter which is controlled by a micro-computer, and, more particularly, it is concerned with a mechanism for checking operations to be conducted at the time of assembly of the above-mentioned electronic typewriter.
FIG. 1 of the accompanying drawing illustrates an external appearance of an electronic typewriter which is in general use. In this Figure of drawing, a reference numeral 1 designates a keyboard as a key input means; a numeral 2 refers to a display unit as a display means for displaying therein print data from the above-mentioned keyboard; and a numeral 3 refers to a printing unit as a printing means for printing the contents displayed in the above-mentioned display unit. Also, in the interior of the above-mentioned electronic typewriter, there are incorporated an editing memory which memorizes, edits, and corrects the print data; a micro-computer as the control means; and so forth. Each and every unit in the electronic typewriter is controlled by this micro-computer. On the other hand, as the general checking items, when assembling the above-mentioned electronic typewriter, there may be contemplated the following: (1) whether the keyboard 1 is capable of performing its regular input operations, or not; (2) whether the display unit 2 performs its regular operations, or not; (3) whether the printing unit 3 performs its regular operations, or not; and so forth. However, considerable time and labour must be expended in carrying out these checkings through manual keyboard operations, which inevitably reflects an increase in manufacturing cost. In order therefore to save time and labour, such checking operations have previously been conducted with the help of an automatic checking sequence to be described in the following. That is to say, at the time of manufacturing the electronic typewriter, a checking program to cause certain definite operations to be done at predetermined sections such as the display unit, the printing unit, etc. is first stored in the program ROM within the main body of the electronic typewriter so as to enable the above-mentioned checking program to be actuated when a particular key is pushed during closure of the power source, thereby carrying out the checking operations to find out whether the definite operations are being done at the above-mentioned predetermined sections, or not. Moreover, since this checking program remains in the program ROM of the finished product, it has so far been the practice that the contents of the checking which should not be effected by users are made inactuable directly from outside by providing checking electrodes on the printed circuit wiring board in the main body of the electronic typewriter to short-circuit the electrodes or to vary a voltage level so as to actuate the checking program. In the above-described conventional method, however, the more functions the electronic typewriter possesses and the more complicated the contents of checking become the larger becomes the scale of the checking program with the consequence that a program ROM of a large capacity is needed. However, since the above-mentioned checking program itself is not used in the ultimate product, the program ROM to store therein the checking program becomes wasteful. Furthermore, in the conventional method of actuating the contents of the checking program which should not be effected by the users, there has been such a problem that no checking could be done at all in the state of the product having been assembled. Further, according to the above-mentioned conventional example, the program ROM is a mask ROM made by writing the program therein at the time of manufacturing the ROM for the purpose of reducing its manufacturing cost at the time of mass production in an industrialized scale of the product, hence the contents of the checking program cannot be changed.